1. Field of the Invention
This invention is directed to air control systems for an internal combustion engine and in particular the invention is directed to a start air control system controlling the air flow to the engine to facilitate consistent clean starts having reduced emission of noxious exhaust gases.
2. Prior Art
Fundamental to starting an internal combustion engine at either high or low ambient temperatures down to minus 30.degree.F is the provision of an ample air-fuel flow during the cranking of the engine and for a short period of time after the initial start to allow the engine to come up to a self-sustaining running speed in the shortest possible time. The air-fuel flow required during this initial phase of the start cycle for quick clean starts is substantially greater than that provided by the fast idle control normally associated with internal combustion engines. The fast idle control only functions to control the curb idle speed of the engine once it has been started and reaches a self-sustaining speed. In order to consistently achieve successful clean starts particularly at low temperatures, a sufficient air-fuel mixture must be supplied during the cranking period to permit the engine to accelerate from the cranking speed to an initial self-sustaining speed in the shortest possible time. Secondly, the engine should be operated at a substantially higher speed than the fast idle speed to purge the intake manifold of the residual starting fuel condensed in the cold intake manifold during cranking, a limit for the substantially higher start speed in the transition between start and idle, and a relatively smooth transition from the substantially higher start speed to the idle speed after the system has been purged to prevent stalling. The limit on the initial start speed during the transition from start to idle is a safety precaution to minimize damage normally attendant high speed operation of a cold engine when the lubricant is relatively viscous and the distribution incomplete.
The prior cold start air for internal combustion engines has been primarily directed to provide the required rich air-fuel mixture during the cranking, initial start, and fast idle warm-up cycle, and has left the requirement for providing the required air-fuel quantity to the operator. Operator manuals for automative vehicles normally contain cold start instructions which include in addition to the proceedure for setting the automatic choke and fast idle accessories, a statement to the effect that the accelerator pedal should be depressed about half-way down and held there until the engine has been successfully started. This proceedure is intended to provide the required quantity of rich air-fuel mixture necessary to start the engine and permit the engine to reach a self-sustaining speed. Admittedly, this proceedure works but is froth with variables which vary from operator to operator as well as from engine to engine. Therefore, successful starting of a cold engine is dependent upon the skill of the operator and can in many instances be damaging to the engine.
The invention is directed to a start air system for internal combustion engines which controls the quantity of air during the cranking and initial start phase of a cold engine, thereby removing the operator variables and substantially increasing the consistency and cleanliness of a successful start. Further because the speed of the engine is controlled between the initial start and idle, the engine is always properly purged of residual starting fuel and excessive wear and damage to the engine due to high speed operation under cold conditions minimized. The consistency and cleanliness of the start provided by the disclosed invention is particularly important in view of the existing and future emission standards being imposed on automotive and commercial vehicles, and especially for future vehicles equipped with thermal reactors.